The present invention concerns bearings for timepieces and more specifically of the shock absorber type. Designers of mechanical watches have for a long time devised numerous devices enabling an arbour to absorb the energy resulting from a shock, particularly a lateral shock, by bearing against a wall of the hole in the base block through which the arbour passes, while allowing a temporary movement of the pivot-shank before it is returned to its rest position under the action of a spring.
FIGS. 1 and 2 illustrate a device, called a double inverted cone device, which is currently used in timepieces found on the market.
A support 1, the base of which comprises a hole 2 for the balance staff 3 ending in pivot-shank 3a, allows a setting 20 to be positioned, in which a pierced stone 4, traversed by pivot-shank 3a, and an endstone 5 are fixedly secured. Setting 20 is held in a recess 6 of support 1 by a spring 10 which, in this example, includes radial extensions 9 compressing endstone 5. Support 1 is a part of revolution including a circular rim 11. This rim 11 is interrupted at two diametrically opposite places by an aperture 12 so as to create two semi-circular rims 11a, 11b. Aperture 12 is arranged partly in the two semi-circular rims 11a, 11b so as to form two return portions. Setting 20 is held in a recess 6 of support 1 by elastic means such as a spring 10 which, in this example, includes radial extensions 9 compressing endstone 5. Spring 10 is of the axial type and is lyre-shaped so as to rest on the return portions of semi-circular rims 11a, 11b. Recess 6 includes two shoulders 7, 7a in the form of inverted cones on which complementary shoulders 8, 8a of setting 20 rest. Said shoulders must be made with a high level of precision. In the event of an axial shock, pierced jewel 4, endstone 5 and the balance staff move and spring 10 acts alone to return balance staff 3 to its initial position. Spring 10 is sized to have a travel limit so that, beyond the limit, the balance staff 3 comes into contact with stop members 14 allowing staff 3 to absorb the shock, which pivot-shanks 3a of staff 3 cannot do without breaking. In the event of a lateral shock, i.e. when the end of the pivot-shank unbalances setting 20 out of its resting plane, spring 10 cooperates with the complementary inclined planes 7, 7a; 8, 8a to re-centre setting 20. These bearings have been sold, for example, under the trademark Incabloc®. These springs may be made of phynox or brass and are manufactured by conventional cutting means.
One drawback of these shock absorber systems is that they are not easy to mount. Indeed, some parts like support 1 and spring 10 must be oriented and manipulated in a certain manner during the mounting operation to enable assembly to occur. Thus, the assembly of the shock absorber system begins with taking a support and then a setting with its jewels. The setting is placed in the recess in the support. Next, a lyre-shaped axial spring is provided. This is manipulated so that it can rest underneath the return portions of semi-circular rims 11a, 11b of the support.
Consequently, a particular manipulation is required to set the spring in place and secure it to the support. As a result, the shock absorber systems must be assembled partly manually since a robot cannot perform such a complex manipulation.
Further, manual assembly is preferred since a human being is capable of instantaneously understanding how the parts of the shock absorber system must be oriented in relation to each other. Indeed, regardless of the shape of the parts, a person is capable of instantly knowing how to manipulate the parts in order to assemble them. Even if a robot is able to differentiate the orientation of one part with respect to another, this requires a more complex and therefore more expensive robot and also requires more time. Consequently, this adversely affects production output.
Thus, total automation of the assembly process is not possible and the method of assembling shock absorber systems is therefore more expensive.
Further, automation of the mounting process may result in the presence of vibrations which propagate in the shock absorber system. These vibrations may cause the parts of the shock absorber system to move so that they are no longer perfectly centred with respect to each other. This potential loss of centring may cause other damage. Indeed, during the mounting of a first part on a second part, a third part required to be placed between the first part and the second part may become pressed between said first and second parts and thus damaged.